This invention relates to a photoresist stripper and more particularly to a composition for removing an organic solvent strippable polymer and/or colloid photoresist mask from a face of a silicon wafer.
Various types of polymer and/or colloid materials are ued to partially mask surfaces for selective etching of those surfaces. The polymers may be natural or synthetic and are resistant to attack by acids. Such masking materials are frequently referred to as resists. Some resists are photosensitive, so that the masking patterns can be photographically produced on the surface to be protected. These latter resists are normally referred to as photoresists. The process of photographically defining a photoresist mask on a metal surface and then etching away the unprotected portions of the metal surface is generally referred to as photoengraving.
Photoresist maskants are used, for example, to engrave complex decorative patterns on a surface, to engrave plates for printing photographs, to define wiring and connection patterns on electronic circuit boards, and to etch oxide layers and metallization patterns for semiconductor devices such as transistors and integrated circuits. It is obviously highly desirable that the photoresist be adherent and highly resistant to attack by the etchant. This permits deep etches, high resolution patterns, etc. Generally, the more resistant the photoresist is to etchant attack, the more difficult it is to remove.
In making semiconductor devices, it is particularly important that the photoresist be especially resistant to attack and yet especially thoroughly removed after it is used. In semiconductor device manufacture, the photoresist is applied to the face of a semiconductive material wafer. The pattern is photographically delineated, and the wafer face selectively etched. The photoresist must then be meticulously removed to prepare the wafer face for subsequent processing steps. No residue or surface contamination should be left on the wafer face. A typical photoresist used in semiconductor device manufacture is KMER (Kodal Metal Etch Resist). This type of photoresist is an organic solvent strippable polymer and/or colloid of the type disclosed in U.S. Pat. Nos. 2,848,328 Hepher; 2,852,379 Hepher et al; 2,940,853 Sangura et al; and 3,458,313 Webb. Photoresists such as these have been removed in the past using a wide variety of strippers, including chlorinated solvents and oxygenated organic materials such as phenols and cresols. U.S. Pat. Nos. 3,335,087 Koers and 3,335,008 Mandell, Jr. disclose adding hydrofluoric acid to such strippers. Phenol-type and cresol-type materials comprise a substantial proportion of popular commercially available strippers. On the other hand, such strippers have special handling and waste disposal requirements I consider desirable to avoid. Such strippers can be avoided, for example, by using special stripping techniques, as for example by using elevated stripper temperatures and/or pressures.
I have found a stripping composition that does not require a mineral acid or an oxygenated organic solvent. Accordingly, it is less caustic and waste disposal is considerably easier. In addition, my composition is highly miscible with water and does not require any special temperatures or pressures for use. It can be used under atmospheric pressure at room temperature, which makes handling of the composition considerably easier. It is thorough in its cleansing action, leaving no recognizable residue or surface contamination, and is simple to use. Moreover, it is stable, low in initial cost and in disposal cost, and can even be reclaimed by distillation.